Training-related changes in neural beta oscillations associated with implicit and explicit motor sequence learning

Many motor actions we perform have a sequential nature while learning a motor sequence involves both implicit and explicit processes. In this work, we developed a task design where participants concurrently learn an implicit and an explicit motor sequence across five training sessions, with EEG recordings at sessions 1 and 5. This intra-subject approach allowed us to study training-induced behavioral and neural changes specific to the explicit and implicit components. Based on previous reports of beta power modulations in sensorimotor networks related to sequence learning, we focused our analysis on beta oscillations at motor-cortical sites. On a behavioral level, substantial performance gains were evident early in learning in the explicit condition, plus slower performance gains across training sessions in both explicit and implicit sequence learning. Consistent with the behavioral trends, we observed a training-related increase in beta power in both sequence learning conditions, while the explicit condition displayed stronger beta power suppression during early learning. The initially stronger beta suppression and subsequent increase in beta power specific to the explicit component, correlated with enhanced behavioral performance, possibly reflecting higher cortical excitability. Our study suggests an involvement of motor-cortical beta oscillations in the explicit component of motor sequence learning.

Note.Generalized linear mixed model with gamma family and log link function.
Note.Type III Sum of Squares Table S1.Summary of the GLMM analysis of the fixed factors condition and block on the reaction times (RTs) of the first training session.The variable 'subject' is used as a random effects grouping factor.GLMM analysis was performed in JASP [1].Note.Type III Sum of Squares Table S3.Summary of the GLMM analysis of the fixed factors condition and session on the reaction times (RTs).The variable 'subject' is used as a random effects grouping factor.GLMM analysis was performed in JASP [1].Note.Type III Sum of Squares Table S5.Summary of the GLMM analysis of the fixed factors condition and session on the performance / accuracy.The variable 'subject' is used as a random effects grouping factor.GLMM analysis was performed in JASP [1].

Fig. S1 .
Fig. S1.Reaction times in the explicit (exp), implicit (imp) and random (ran) condition within the first session.The mean RT per sequence trial is shown, while a trial consists of 8 key presses.A sliding window approach was used to smoothen the curves (moving average smoothing, n=3).The shaded area represents the 95 % confidence interval.

Fig. S2 .
Fig. S2.Reaction times in the explicit (exp), implicit (imp) and random (ran) condition across sessions (b) (n=25 subjects).The mean RT across the 5 experimental sessions (i.e.average of 8 key presses) is shown per condition.The individual points represent the mean RT for one subject per session per condition.Only correct sequences are included.While the first session consists of 4 blocks, sessions 2 to 5 consist of 2 blocks, with 18 sequence trials per condition per block.The bars represent the 95 % confidence intervals.

Fig. S3 .
Fig. S3.Reaction time (RT) contrasts between experimental conditions over the course of training sessions (n=25 subjects).a) Shows the difference between RTs in the random and implicit condition.b) shows the difference between RTs in the random and explicit condition.c) shows the difference between RTs in the implicit and explicit condition.The vertical bars represent the 95 % confidence intervals.Each point in the background data represents the mean RT for one individual subject in this specific contrast and session.

Fig. S4 .
Fig. S4.The accuracy in the explicit (exp), implicit (imp) and random (ran) condition across all 5 experimental sessions (n=25 subjects).The performance in a sequence trial was calculated as the actual number of correct key presses divided by 8, which is the maximal number of correct key presses per sequence trial.The individual points represent the mean accuracy for one subject per session per condition.Vertical lines represent the 95 % confidence

Fig. S5 .
Fig. S5.Event-related spectral perturbations (ERSPs) in the explicit, implicit and random condition (left) and differences in the ERSPs between experimental conditions (right).The ERSPs are grouped by the first and second half of session 1 and session 5 (n=25 subjects).a) The ERSPs for the explicit, implicit and random condition are given in dB, relative to a baseline (-1000 to -250 ms before the start of the sequence trial).Background data points represent the mean ERSP for individual subjects, split by session half and condition.Statistical comparisons using the Wilcoxon signed rank test are depicted with gray vertical lines, with * representing p ≤ .05,** p ≤ .01 and *** representing p ≤ .001(Bonferroni corrected for multiple comparisons).b) ERSP difference between the explicit (exp, blue) and random and between the implicit (imp, orange) and random condition.The ERSP differences are given in dB, relative to a baseline (-1000 to -250 ms before the start of the sequence trial).The random control condition was subtracted from the sequence conditions, such that negative ∆ ERSPs indicate stronger beta power suppression, while positive values indicate less beta power suppression, compared to the random condition.Background data points represent the mean ERSP differences for individual subjects, split by session half and contrast (exp: explicit-random; imp: implicit-random).c) ERSP difference between the explicit and implicit condition.The ERSP differences are given in dB, relative to a baseline (-1000 to -250 ms before the start of the sequence trial).The implicit condition was subtracted from the explicit condition, such that negative ∆ ERSPs indicate stronger beta power suppression in the explicit condition, while positive values indicate stronger beta power suppression in the implicit condition.Background data points represent the mean ERSP differences for individual subjects, split by session half.Sessions are separated by a dark-gray vertical line emphasizing different recording days.The black vertical bars represent the 95 % confidence intervals.

Table S4 . Wilcoxon signed-rank test results for RTs across sessions and conditions.
interaction between session and condition for all combinations of conditions in each session.The Wilcoxon W statistic (W-val), the uncorrected p-values (p-unc) of the two-tailed test and the Bonferroni corrected p-values (p-corr) are reported.